Does EVERYTHING cause cancer?

26 June 2011

This week’s question comes from Frank Uyeda in San Diego, California:

“X may cause cancer” seems to be plastered on the side of just about everything these days. It seems like most peoples’ reactions to such things are strictly fear-driven. How should we think about and quantify the risk of cancer caused by various products/activities (i.e. BPA in waterbottles, X-ray machines in airports, radiation from traveling on airplanes, living near power lines, sun bathing). In addition, cancers caused by some of these things will be easier/harder to treat. Which things put me at the highest risk of hard to treat cancer?

Hi Frank,

Did you know that breathing also causes cancer? I’m not kidding. Oxidative phosphorylation in all of our cells can lead to free radicals, damage DNA, and spark cancer. Now, I’m not holding my breath or anything. Pretty much anything can cause cancer in certain amounts, or when rhetorically spun.

I think you’re driving at a very good point. The world we live in is not binary, and as a result additional questions arise: Even if X causes cancer, how much? How many more people will present with disease? And of those with the disease, what percent increase in incidence will be the aggressive versions of the disease? Even so, is the increased risk worth worrying about because it is so small and pales in comparison to other things?

With perhaps the exception of ionizing radiation, it’s very hard to quantify how much various activities and diet can contribute to cancer risk. For ionizing radiation, this chart does a good job of putting things into perspective for airport x-rays and travelling on airplanes: XKCD comic

What about difficult to treat cancers? Leukemias and lymphomas (cancer of the blood) aside, once disease has progressed to the point where it spreads, any other type of cancer becomes very difficult to treat. I will discuss what makes certain cancers harder to treat than others in another article.

I’m going put things in perspective with a dangerously un-scientific sweeping generalization: the vast majority of things you hear are sensationalism. A lot of the correlation studies that are so popular to broadcast in the media have very weak correlation, or even if the correlation is strong, the effect is so small as to seldom ever affect anyone. In my opinion, the Federal Drug Administration and the World Health Organization are a little trigger happy with labeling something a carcinogen. Relative to the flurry of things with a possible “cancer link” there are actually very few things that have an established causal (as opposed to correlative) relationship to cancer development. And even for the things that do (like ionizing radiation) the amount of exposure to the average person is so small as to pale in comparison to other influencers of cancer development. (again, see XKCD comic)

To put the flurry of sensational cancer-causing claims in perspective, I feel it is a better use of everyone’s physical and mental energy to focus on the things that have a STRONG correlation with cancer development. For the sake of brevity, I decided to narrow it down to three critical risk factors:

1) Sun exposure
2) Smoking status
3) Age

1) Lifetime sun exposure mixed with skin fairness is good at predicting skin cancer risk. The mechanism is well understood (see previous article on radiation) and can be successfully mitigated (UV protection) based off the experimental models developed by scientists. Cumulative sun exposure over time causes cancer.

2) “It remains an astonishing, disturbing fact that in America – a nation where nearly every drug is subjected to rigorous scrutiny as a potential carcinogen, and even the bare hint of a substance’s link to cancer ignites a firestorm of public hysteria and media anxiety-one of the most potent and common carcinogens known to humans can be freely bought and sold at every corner store for a few dollars.” – Siddhartha Mukherjee in the Emperor of All Maladies. There is no such thing as dogma in science, but the causal link between smoking and cancer development is one of the strongest in the history of medicine. Cigarettes are one of the few items on the market that, when used as per the instructions on the label, WILL kill you.

3) Often overlooked in cancer risk is the importance of age. Last time I checked, there was no cure for aging. My opening comment on breathing causing cancer is actually more true than most of the sensationalism in the media. As I discussed in a previous article, cancer is an age-related disease and simply being alive puts one at a higher cumulative effect of developing cancer, even in the hypothetically most non-carcinogenic environment. In that respect, cancer can be seen as a “natural” side effect of being alive. Curiously, there are certain actions that can slow one’s biological aging, my favorite being consistent aerobic exercise. I touched upon this in a previous article on cancer prevention. The take-home message is that as one accumulates biological age, it’s a good idea to get more frequent (annual) check-ups and be more proactive in discussing cancer with personal physicians. Aside from not getting cancer at all, catching the disease early is the next best thing.

These are the bases that need to be covered and understood by the masses in developed countries. A lot of other risk factors that I discuss in this blog are icing on the cake, and many of the studies heard in the news are either weakly correlative at best, and fake at worst. In fact, I would argue that the cancer hysteria in the news is often so overplayed that it is dangerous in itself for the undue stress and anxiety bestowed upon listeners. Again, this is a dangerously un-scientific sweeping generalization, but in this instance there is a lot of mis-information and non-information disseminated by the media that does nothing but spread headaches.